Fiber-to-waveguide optical interface devices and coupling devices with lenses for photonic systems

ABSTRACT

An optical interface device for a photonic integrated system includes a plug and a receptacle. The receptacle is operably arranged on a PIC that supports waveguides. The plug operably supports optical fibers. The receptacle and plug are configured to operably engage to establish optical communication between the optical fibers and the waveguides. A tab on the receptacle is configured to constrain longitudinal motion while allowing for lateral motion of the receptacle to adjust its position relative to the PIC to optimize alignment. The plug can include a spacer sized to fit within a recess defined by the tab to further facilitate alignment. The plug can also include lenses to establish the optical communication between the optical fibers and the waveguides. The receptacle and plug can be engaged and disengaged in a manner similar to conventional electrical connectors.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present specification is a continuation of U.S. patent applicationSer. No. 15/251,342 filed on Aug. 30, 2016 and entitled“FIBER-TO-WAVEGUIDE OPTICAL INTERFACE DEVICES AND COUPLING DEVICES WITHLENSES FOR PHOTONIC SYSTEMS,” which is incorporated by reference hereinin its entirety.

FIELD

The present disclosure relates to integrated photonics, and inparticular relates to a fiber-to-waveguide optical interface devices andcoupling devices with lenses for photonic systems.

BACKGROUND

Photonic systems are presently used in a variety of applications anddevices to communicate information using light (optical) signals.Photonic systems typically include photonic integrated circuits (PICs),which are analogous to electronic integrated circuits in that theyintegrate multiple components into a single material where thosecomponents operate using light only or a combination of light andelectricity. A typical PIC has a combination of electrical and opticalfunctionality, and can include light transmitters (light sources) andlight receivers (photodetectors), as well as electrical wiring and likecomponents that serve to generate and carry electrical signals forconversion to optical signals and vice versa.

A PIC includes one or more optical waveguides that carry light inanalogy to the way metal wires carry electricity in electronicintegrated circuits. Just as the electricity traveling in the wires ofan electronic integrated circuit carries electrical signals, the lighttraveling in the waveguides of a PIC carries optical signals.

To transmit the optical signals from the PIC to a remote device, theoptical signals carried by a waveguide in the PIC need to be transferredor “optically coupled” to a corresponding optical fiber connected to theremote device. Coupling light from a planar waveguide to an opticalfiber is achieved either through the surface of the PIC via surfacecorrugated gratings or via embedded total internal reflection mirrors,or from the edge via proximity coupling or edge coupling, also referredto as “butt coupling.”

Current edge coupling techniques involve forming a permanent bondbetween the optical fibers and the waveguides. Thus, there is anunresolved need for improved edge coupling.

SUMMARY

An aspect of the disclosure is a coupling device for an opticalinterface device for a PIC assembly that includes: a body having a frontend, a back end and a lower surface; at least one alignment feature atthe front end of the body; at least one bore that runs from the back endand either through to the front end or that terminates adjacent thefront end, the at least one bore sized to accommodate at least oneoptical fiber; and at least one lens at the front end and operablyaligned with the at least one bore.

Another aspect of the disclosure is an optical interface device thatincludes the coupling device described above, wherein the couplingdevice defines a first coupling device and operably supports at leastone optical fiber in the at least one bore; a PIC assembly having a PICthat supports at least one waveguide having an end face and having asecond coupling device operably arranged with the PIC and having a frontend; and wherein the first and second coupling devices are configured tooperably engage so that the at least one waveguide supported by the PICis in optical communication with the at least one optical fiber of thefirst coupling device through the at least one lens on the front end ofthe first coupling device.

Additional features and advantages are set forth in the DetailedDescription that follows, and in part will be readily apparent to thoseskilled in the art from the description or recognized by practicing theembodiments as described in the written description and claims hereof,as well as the appended drawings. It is to be understood that both theforegoing general description and the following Detailed Description aremerely exemplary, and are intended to provide an overview or frameworkto understand the nature and character of the claims.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings are included to provide a furtherunderstanding, and are incorporated in and constitute a part of thisspecification. The drawings illustrate one or more embodiments andtogether with the Detailed Description serve to explain principles andoperation of the various embodiments. As such, the disclosure willbecome more fully understood from the following Detailed Description,taken in conjunction with the accompanying Figures, in which:

FIG. 1 is an elevated view of an example photonic system that includes aPIC assembly and an optical interface device that has a first couplingdevice in the form of a plug and a second coupling device in the form ofa receptacle;

FIG. 2A is a partially exploded view of the example photonic system ofFIG. 1, wherein the plug is disconnected from the receptacle;

FIG. 2B is a close-up front elevated view of the PIC assembly of thephotonic system of FIGS. 1 and 2A;

FIG. 3A is an elevated view of an example plug of the optical interfacedevice shown in FIGS. 1, 2A and 2B;

FIG. 3B is a front on view of an example plug of the optical interfacedevice shown in FIGS. 1, 2A and 2B;

FIG. 3C is a side view of an example plug of the optical interfacedevice shown in FIGS. 1 and 2 and illustrates an example wherein theferrule body of the plug includes an integrally formed spacer with anupward-facing ledge;

FIG. 3D is similar to FIG. 3D and shows an example of a spacer formed asa separate piece from the ferrule body of the plug;

FIG. 4A is front elevated view of an example PIC assembly similar toFIG. 2B and showing an example configuration of a receptacle, PIC,interposer and printed circuit board, wherein the z-motion of thereceptacle relative to the PIC is constrained by the tab sections;

FIGS. 4B through 4D are front-on views of example PIC assemblies showingthree different example configurations of the receptacle tab;

FIG. 5 is a partially exploded side view of an example optical interfacedevice showing an example configuration wherein the plug and receptaclerespectively include complementary spacers;

FIG. 6A is a front on view and FIG. 6B is a side view of an example tabthat is added to the front end of the receptacle body;

FIG. 7A is similar to FIG. 6A, except that the thickness of the tab isgreater than the thickness of the plug spacer in order to provide aselect spacing between the end faces of the optical fibers of the plugand the waveguides of the PIC;

FIG. 7B shows the plug and receptacle of FIG. 7A operably engaged;

FIG. 7C is similar to FIG. 7A and illustrates an example wherein thefront end of the plug is flat;

FIG. 7D is similar to FIG. 7C and illustrates an example wherein thefront end of the plug includes lenses configured to optically couplelight between the fibers of the plug and the waveguides of thereceptacle;

FIG. 7E is similar to FIG. 7D and illustrates an example where the frontend of the plug includes a spacer that includes lenses to opticallycouple light between the fibers of the plug and the waveguides of thereceptacle;

FIG. 8A is a top-down partially exploded view of an example opticalinterface device, illustrating how the tab can compensate for an errorin the shape of the front end of the receptacle body;

FIG. 8B is similar to FIG. 4A and illustrates an embodiment wherein thereceptacle body includes one or more recesses in the lower surface tofacilitate securing the receptacle to the underlying PIC;

FIG. 9A is a top-down partially exploded view of an example two-partreceptacle along with an example two-part tab;

FIG. 9B is a front-on view of an example PIC assembly showing thetwo-part receptacle and the two-part tab;

FIG. 9C is similar to FIG. 9A and shows an example configuration of atwo-part receptacle and a one-part (unitary) tab;

FIG. 10A and FIG. 10B are top-down views of templates used to formexample U-shaped tabs in a sheet of spacer material; and

FIG. 11 is a front-on view of an example tab configured for use with anMTP type of plug.

DETAILED DESCRIPTION

Reference is now made in detail to various embodiments of thedisclosure, examples of which are illustrated in the accompanyingdrawings. Whenever possible, the same or like reference numbers andsymbols are used throughout the drawings to refer to the same or likeparts. The drawings are not necessarily to scale, and one skilled in theart will recognize where the drawings have been simplified to illustratethe key aspects of the disclosure.

The claims as set forth below are incorporated into and constitute partof this Detailed Description.

Cartesian coordinates are shown in some of the Figures for the sake ofreference and are not intended to be limiting as to direction ororientation.

In the description below, longitudinal or axial movement is in thez-direction while lateral movement is in the x-direction and/or they-direction.

Photonic System and PIC Assembly

FIG. 1 is an elevated view of an example photonic system 6, while FIG.2A is an elevated and partially exploded view of the photonic system ofFIG. 1. FIG. 2B is a close-up elevated view of the receptacle portion ofthe photonic system 6. The photonic system 6 includes a PIC assembly 10.The PIC assembly 10 includes a PIC 20 and a substrate 60 that operablysupports the PIC. In an example, substrate 60 includes an interposer 70and a printed circuit board 80, in which case PIC 20 is operably mountedto the interposer 70, which is operably mounted to the PCB 80. Theinterposer 70 is configured to provide electrical connections betweenPIC 20 and PCB 80. The interposer 70 can be made of a variety ofdifferent materials, including glass or silicon.

The photonic system 6 also includes an optical interface device 100which includes a first coupling device 200 and a second coupling device300, wherein the first and second coupling devices are configured tooperably engage and disengage. The first coupling device 200 is shown inFIG. 2A in the form of a plug while the second coupling device 300 isshown in FIGS. 2A and 2B as being in the form of a receptacle operablyarranged on PIC 20. In other embodiments, the first coupling device 200can be in the form of a plug and the second coupling device 300 can bein the form of a receptacle. In the discussion below, first couplingdevice 200 is referred to as a plug while the second coupling device 300is referred to as a receptacle for ease of discussion.

In an example, the plug 200 and receptacle 300 are maintained in anoperably engaged configuration using any one of a number of latchmechanisms (not shown) known in the art for connectors, such asdisclosed in U.S. Pat. Nos. 6,565,262 and 7,377,699 and 5,254,014, whichare all incorporated by reference herein in their entirety.

The main components of photonic system 6 and the optical interfacedevice 100 are now discussed in greater detail below.

Example Plug

FIG. 3A is an elevated view, FIG. 3B is a front on view and FIG. 3C isan example side view of plug 200. Plug 200 includes a ferrule body(“ferrule”) 201 having a front side or front end 202, a back side orback end 204, upper and lower surfaces 212 and 214, a central portion216, and opposite edges (sides) 218. In an example, ferrule 201 ismonolithic. The plug 100 operably supports an array 230 of opticalfibers 232 each having core 233 a, a cladding 233 b surrounding the core(see close-up inset in FIG. 3A). Each optical fiber 232 has an end face234. In an example, the array 230 of optical fiber 232 runs through asingle elongate bore 228 as shown in FIG. 3A. In another example, eachoptical fiber 232 runs through respective bores 228, as shown in FIG.3B. More generally, ferrule 201 includes one or more bores 228. The oneor more bores are formed in central portion 226 of ferrule 201 andreside in an x-z bore plane 228P. In an example where each fiber 232runs through a respective bore 228, each of the bores has a circularcross-sectional shape that is slightly larger than the diameter of thefiber. In an example, end faces 234 of fibers 232 are substantiallyco-planar with front end 202. The optical fibers 232 in array 230 definea pitch p_(F). Example optical fibers 232 have a diameter of either 80microns or 125 microns. Other diameters for fibers 232 can also beemployed.

The plug 200 also includes at least one alignment feature 240. In anexample, two spaced apart alignment features 240 are employed. In anexample, alignment feature 240 resides adjacent upper surface 212 andabove bore plane 228, as shown in FIG. 3A. In examples, alignmentfeature 240 is in form of an alignment pin (to define the plugconfiguration, as shown) or an alignment hole (to define a receptacleconfiguration). By way of example, the discussion below refers to anembodiment having two spaced apart alignment features 240 in the form ofalignment pins that reside in an x-z alignment-feature plane 240P (seeFIG. 3B). The y-distance between alignment feature plane 240P and boreplane 228P is denoted DY1. As shown in FIG. 3A, plug 200 has an overallheight dimension h1, an overall length dimension l1 and an overall widthdimension w1.

The array 230 of optical fibers 232 of plug 200 is configured tooptically couple to the array of waveguides supported by PIC 20 of PICassembly 10 when plug 100 is operably coupled to receptacle 300 of thePIC assembly, as explained below. Thus, in an example, the optical fiberpitch p_(F) is equal to the waveguide pitch p_(W), and the numberoptical fibers 232 is equal to the number PIC assembly waveguides.

The side view of FIG. 3C shows an example wherein ferrule 201 includes aprotrusion or “spacer” 250 that extends from front end 202 adjacentlower surface 214 and that defines an upward facing ledge 252. Thespacer 250 facilitates the mechanical engagement, including thealignment and spacing of plug 200 relative to receptacle 300, asdescribed below. The spacer 250 has a thickness TP as measured in thez-direction relative to front end 202. As spacer 250 is associated withplug 200, it is referred to hereinafter as plug spacer 250.

In an example, plug spacer 250 can be formed as part of a monolithicferrule 201, such as shown in FIG. 3C. In another example, plug spacer250 can be formed as one or more separate parts (i.e., one or moreseparate pieces) added to the front end 202 of the ferrule 201, asillustrated in FIG. 3D. The plug spacer need not extend all the waybetween sides 218 of ferrule 201.

PIC Assembly

FIG. 4A is a front elevated view of an example PIC assembly 10, andFIGS. 4B through 4D are front-on views of two different exampleconfigurations of the PIC assembly. As noted above, PIC assembly 10includes PIC 20, which has front and back ends 22 and 24, opposite upperand lower surfaces 25 and 27, and opposite sides 28. The PIC 20 can beformed from silicon, indium phosphide or glass.

The PIC 20 supports an array 30 of optical waveguides (“waveguides”) 32that run longitudinally in the z-direction down a center portion of thePIC. Each waveguide 32 has an end face 34 that terminates substantiallyat front end 22. In an example, end faces 34 terminate near lowersurface 27, as shown in FIG. 1. In other examples, end faces 34terminate near upper surface 25. Generally, end faces 34 terminateanywhere between upper surface 25 and lower surface 27. In an example,waveguides 32 are made of glass. In another example, the waveguides 32are made of silicon. In an example, waveguides 32 comprise channelwaveguides. Also in an example, waveguides 32 are single mode. The array30 of waveguides 32 has the aforementioned waveguide pitch p_(W).

The PIC 20 can also include other components that are not shown, such aslasers, photodetectors, metal wiring, optical redirecting elements,electrical processing circuitry, optical processing circuitry, contactpads, etc., as is known in the art. In an example, PIC 20 is formedmainly from silicon (i.e., is silicon-based) and constitutes a siliconphotonics (SiP) device. In another example, PIC 20 is formed mainly fromglass, (i.e., is glass-based) and constitutes a passive planar lightwavecircuit. The PIC 20 can also be formed from other semiconductormaterials known in the art. The PIC 20 can function a direct-detectionor coherent-detection transceiver, a splitter, a fan-out, a tap coupler,a multiplexer/demultiplexer, a laser array, etc.

Example Receptacles

As noted above, PIC assembly 10 supports receptacle 300 operablyarranged relative to PIC 20. In an example, receptacle 300 has acoefficient of thermal expansion (CTE) close to the PIC material (e.g.,within 50% or within 20% or within 10%) so that there is little movementor stress build-up between the receptacle and PIC 20 during hightemperature operation. In an example, receptacle 300 can be secured toPIC 20 using a suitable securing material, such as an epoxy or likebonding adhesive, as explained in greater detail below.

With reference again to FIGS. 4A through 4D, the receptacle body 301 hasa front end 302, a back end 304, an upper surface 312 and a lowersurface 314, a central portion 316 and opposite sides or edges 318. Inexamples, receptacle body 301 can be formed form a molded polymer or aglass. With reference to FIG. 8B introduced and discussed below, in anexample, receptacle 300 has a generally rectangular body 301 with anoverall width dimension w2, an overall length dimension l2 and anoverall height dimension h2.

In an example, receptacle 300 includes at least one alignment feature340. FIG. 4A shows an example that includes two alignment features 340formed in front end 302. In an example, alignment feature 340 is in theform of two alignment holes configured to receive the two alignment pins240 of plug 200. In an example such as shown in FIG. 4B, one alignmenthole 340 is elongate to avoid over-constraining the mating of receptacle300 to plug 200 in the x-direction and to allow for relative movementdue to a CTE mismatch between plug 200 and receptacle 300. This examplealignment configuration can be particularly useful if receptacle 300 ismade from a non-compliant material, such as glass. The at least onealignment feature 340 can also be offset with respect to an axis ofsymmetry of the fiber array. This is beneficial in reducing the thermalmovement due to thermal expansion since the distance from the axis ofsymmetric thermal movement is reduced. In one configuration the circular(non-elongate) alignment hole 340 is centered on array 30 of waveguides32 of PIC 20, but other configurations are possible.

In an example, receptacle 300 includes at front end 302 a tab 320 thatin an example includes at least one downwardly depending tab section 321that extends beyond lower surface 314. In an example, tab 320 defines arecess 322 configured to accommodate spacer 250 of plug 200. In anexample, tab 320 includes at least one alignment feature 340, whichfurther in an example can be in tab section 321. In the exampleconfiguration illustrated in FIG. 2A, tab 320 is integrally formed with(i.e., is part of) a monolithic receptacle body 301, with tab sections321 downwardly depending to cover at least a portion of front end 22 ofPIC 20. In another example best seen in FIG. 2B, tab 320 is formed as asingle, separate part as illustrated by the dashed line DL in FIG. 2B.The tab 320 can also be formed as two separate parts that each define aseparate tab section 321, as discussed below in connection with FIGS. 9Aand 9B. In the example discussed below, tab 320 has a U-shape defined bytwo tab sections 321 and recess 322.

In FIG. 4B, tab 320 is configures so that the two tab sections 321extend into corresponding recesses 26 in upper surface 26 of PIC 20 andcan be used to perform alignment of receptacle 300 with respect to theunderlying PIC. The tabs 320 can be configured to form a recess 322between lower surface 314 and upper surface 25 of PIC20. In FIG. 4C, tabsections 320 are configured to extend into substrate 60. In an example,tab sections 320 are configured to extend onto the front surface ofsubstrate 60. In an example, a layer of securing material 380 such as anepoxy can be employed to secure receptacle body 301 to underlying PIC20.

FIG. 4D is similar to FIGS. 4B and 4C and shows an example where tab 320is formed such that the recess 322 is in the form of an aperture sizedto accommodate spacer 250 of plug 200.

With reference again to FIG. 4A, it is noted that the z-motion (i.e.,axial or longitudinal motion) of receptacle 300 relative to PIC 20 isconstrained by tab sections 321 that extend in front of and are incontact with front end 22 of the PIC. This allows for lateral (i.e., xand y movement of receptacle 300. The lateral movement in they-direction (i.e., vertical movement) allows for lower surface 314 ofthe body 301 of receptacle 300 to be spaced apart from the PIC topsurface 25 in the y-direction by an amount selected to optimizealignment between the at least one waveguide 32 of PIC 20 and at leastone optical fiber 232 of plug 20 when forming an optical interfacedevice. The select spacing can be fixed using for example securingmaterial 380 disposed between PIC top surface 25 and lower surface 314of body 301 of receptacle 300.

As discussed above in connection with FIG. 3B, the y-distance betweenalignment feature plane 240P and bore plane 228P is denoted DY1. Thedistance DY1 depends on the location of waveguides 32, which depends onthickness th of the PIC and where the waveguides are supported by thePIC, e.g., on upper surface 25, on lower surface 27, or somewherebetween. Since it is desired that a single plug 200 be able to mate withdifferent receptacles 300, in an example, the distance DY1 can bedesigned to be the maximum needed for any configuration of PIC 20.

As explained above, the elevation (i.e., y-position) of receptacle 300on PIC 20 can be adjusted so that fibers 232 are aligned with waveguides32. In an example illustrated in FIGS. 4A, 4B and 4C, the layer ofsecuring material 380 between receptacle 300 and PIC 20 is used to fillthe gap between lower surface 314 of receptacle 300 and upper surface 25of PIC 20 and secure the receptacle to the PIC 20 when fibers 232 andwaveguides 32 are aligned.

It is noted here that securing material 380 need not define the size ofthe gap between the lower surface 314 of receptacle 300 and the uppersurface 25 of PIC 20 when fibers 232 and waveguides 32 are aligned. Inan example, receptacle 300 is engaged with plug 200 and is then adjustedin the x-y plane to align waveguides 32 and fibers 232 while tab section320 constrains motion in the z-direction. This alignment adjustmentcreates the gap. There is no z-movement because tab sections 320restriction z-direction movement. The restriction of z-movement by tab329 is an advantage since simplifies fiber-to-waveguide alignment tomovement in just the x and y directions.

Additional Receptacle Tab and Plug Spacer Configurations

FIG. 5 is a partially exploded side view of optical interface device 100that shows an example configuration wherein tab 320 defines a downwardfacing ledge 352. The tab 320 is shown by way of example as a separatepart that is added to the front end 302 of body 301 of receptacle 300.The plug 200 includes the aforementioned plug spacer 250 with upwardfacing ledge 252. The downward facing ledge 352 of tab 320 is configuredto make contact with upward facing ledge 252 of plug spacer 250 whenplug 200 and receptacle 300 are operably engaged. The downward facingledge 352 along with tab sections 321 of tab 320 aid in alignment ofoptical fibers 232 of plug 200 to waveguides 32 of PIC 20 by restrictingmovement of the plug when the plug is engaged with receptacle 300. Italso allows receptacle 300 to be moved in the vertical direction (i.e.,y-direction) to enable optical fibers 232 and waveguides 32 to beoptimally aligned. The tab 320 has a thickness TR as measured in thez-direction. The tab 320 can be considered a counterpart to thereceptacle spacer and could also be referred to as a “receptacle spacer.

In an example where tab 320 is a separate component added to receptaclebody 301, it can be fabricated from fusion glass. FIG. 6A is a front-onview and FIG. 6B is a side view of an example tab 320 in the form of aplate that can be attached to front end 302 of receptacle body 301. Thedashed line DL in FIG. 6A schematically illustrates where tab section321 begins, i.e., where tab 320 would extend to cover front end 22 ofPIC 22, as shown in FIG. 5.

The tab 320 can include one or more holes 354 that align with one ormore alignment features 340 formed in receptacle front end 302. Theholes 354 need not have the exact same diameter as alignment features340 and in an example are slightly larger to provide clearance foralignment features (e.g., alignment pins) 340 of plug 300.

FIGS. 7A and 7B are similar to FIG. 5 and illustrate the use of plugspacer 250 and tab 320 to define a gap G with a gap spacing GS betweenwaveguide end faces 34 and optical fiber end faces 134 when the plug 200and receptacle 300 are operably engaged. In an example, this isaccomplished by making the thickness TR of tab 320 greater than thethickness TP of plug spacer 250, i.e., TR>TP.

In an example, the gap spacing GS is in the range 0<GS<2.1 mm. Inanother example, the gap spacing GS is either in the range 0<GS<65microns or 270 microns<GS<2100 microns. In another example, the gapspacing GS is within (i.e., less than) the Rayleigh range of a Gaussianbeam propagating between each waveguide end face 34 and opposing opticalfiber end face 134. FIG. 7C is similar to FIG. 7A and illustrates anexample wherein the front end 202 of ferrule 201 of plug 200 is flat,there is no plug spacer 250 so that TP=0.

To avoid physical contact and possible damage to the waveguide end faces34 and the fiber end faces 134 while still allowing for direct end-facecoupling, gap G can have a minimal gap distance GS, e.g., 0<GS<65microns (e.g., 5 microns). For relatively small gap spacings GS, anindex matching gel can be placed in the gap to avoid loss from Fresnelreflection. To expand the (Gaussian) optical beam that travels betweenwaveguide end faces 34 and fiber end faces 232 and to improve thelateral misalignment tolerance and resistance to dust other microscopicdebris that can obstruct the optical beam transmitted over gap G, thegap spacing GS can be in the larger end of the range, e.g., 270microns<GS<2100 microns, or can be less than the aforementioned Rayleighrange.

FIG. 7D is similar to FIG. 7C and illustrates an example wherein for arelative large gap spacing GS, front end 202 of plug 200 includes atleast one lens 60 configured to optically couple light between at leastone fiber 232 of plug 200 and at least one waveguides 32 of receptacle300 across gap G. In an example, lens or lenses 60 can be gradient-indexlenses, molded lenses, etc. In an example, lens or lenses 60 can beformed in a portion of ferrule 201 and the end faces of fibers 32terminate at an end of bore 228 within the ferrule body. In an example,lens or lenses 60 can be formed to be substantially flush with front end202 of ferrule 201. In an example, lens or lenses 60 can be formed as anintegral and monolithic part of the ferrule during the ferrule-formingprocess (e.g., during a mold process). The lens or lenses 60 can also beadded to ferrule 201 at front end 202. In an example, lens or lenses 60can be made of a different material than ferrule 201. In an example,lens or lenses 60 can be supported by a plate or like support membersuch as plug spacer 250 attached to ferrule front end 202, as shown inFIG. 7E. In an example, lens or lenses 60 can be made of glass.

FIG. 8A is a top-down partially exploded view of optical interfacedevice 100 illustrating the use of tab 320 to increase the tolerance tosmall angular misalignments between receptacle 300 and ferrule 201 ofplug 200. In an example, alignment fiducials 374 can be formed on uppersurface 312 of body 301 for performing alignment of receptacle 300 andthe underlying PIC 20 if the receptacle is made of a transparentmaterial such as Ultem or glass. FIG. 1 also shows example alignmentfiducials 374 on plug 200 and receptacle 300. Alignment fiducials 374can be formed using a variety of known techniques, such asphotolithographic techniques, and can have a variety of shapes, sizesand configurations known in the art.

If front end 302 of receptacle body 301 has a slight shape errorrelative to sides 318, then tab 320 can be arranged to compensate forthis shape error. The shape error shown in FIG. 8A creates an angularmisalignment. The ferrule alignment features (e.g., alignment pins) 240can be used as a fixture to insure that tab 320 is substantially flatand parallel to the ferrule front end 202. In an example, securingmaterial 380 is used to secure tab 320 to front end 302 of receptaclebody 301. In this example, the securing material 380 can fill any gap382 between front end 302 and the tab 320 due to the shape error.

FIG. 8A also shows an example wherein receptacle body 301 includesthrough holes 388 that run in the z-direction and connect the upper andlower surfaces 312 and 314. The through holes 388 can be used to insertsecuring material 380 (e.g., an epoxy) to secure receptacle 300 tounderlying PIC 20.

FIG. 8B is similar to FIG. 4A and illustrates an embodiment whereinreceptacle body 301 includes one or more recesses 390 in lower surface314. The one or more recesses 390 can serve as a reservoir for securingmaterial 380 when securing receptacle 300 to upper surface 22 of PIC 20.In an example, the one or more recesses 390 can be in the form oflongitudinal grooves as shown. Other shapes and orientations for the oneor more recesses 390 can also be used. In other embodiments, standardmicroelectronics packaging techniques are used to secure receptacle 300to PIC 20.

FIG. 9A is a top-down partially exploded view of an example receptacle300 wherein the receptacle body 301 is constituted by two separate parts301A and 301B that are elongate in the z-direction. Also shown is anexample tab 320 formed using two separate tab parts 320A and 320B. Inanother example, the separate tab parts 320A and 320B can be formedintegral with receptacle body parts 301A and 301B, respectively.

FIG. 9B is a front-on view of an example PIC assembly 20 that utilizesthe example two-part receptacle 300 and two tab parts 320A and 320B ofFIG. 9A. FIG. 9B also shows an example of alignment fiducials 374 formedthe two tab parts 320A and 320B

One benefit to the two-part configuration of receptacle 300 is that itreduces adverse effects of any CTE mismatch between the receptacle andthe underlying PIC 20. Because the two parts 301A and 301B of receptaclebody 301 are separately secured to PIC 20, adverse effects of a CTEmismatch between the two parts and the PIC are reduced because theamount of material that resides between alignment features 340 isreduced as compared to a unitary (single-part) receptacle 300. Thisreduction in adverse effects of a CTE mismatch is particularly effectivewhen receptacle body 301 is made of a polymer material, which has ahigher CTE than silica or silicon.

FIG. 9C is similar to FIG. 9A and shows an example embodiment whereintab 320 is unitary, i.e., is a single part, that attaches to therespective front ends 302 of the receptacle body parts 301A and 301B.

Forming the Receptacle

In an example, receptacle body 301 has a symmetry designed to facilitatethe formation of receptacle 300. An example symmetric receptacle body301 has a U-shaped cross section. The U-shape can be squared off or canhave rounded edges. The techniques used for forming receptacle 300include at least one of a polymer extrusion process, a glass extrusionprocess and a redraw process. A redraw process allows for receptaclebody 301 to be formed to micron and even sub-micron tolerances. Suchfabrication accuracy allows for passive alignment of receptacle 300 toPIC 20 if waveguides 32 are well-defined with respect to upper surface22 of the PIC, i.e., by using the PIC upper surface as a reference datumfor the y-dimension. Alignment features on receptacle 300 and PIC 20 canbe used for alignment in the x-z plane. The recesses 390 discussed abovecan also be readily formed using the aforementioned extrusion and redrawprocesses.

Forming the Tab

As discussed above, tab 320 can be formed as a separate part fromreceptacle body 301, i.e., as a tab. In an example, tab 320 can beformed using a sheet of material, e.g., a sheet of glass. Example typesof glass include thermally strengthened glass or an ion-exchanged glass,such as GORILLA® glass from Corning, Inc. An advantage of using a glasstab 320 is that any CTE mismatch with respect to interposer 70 is notsubstantial, especially when the interposer is also made of glass orsilicon.

FIG. 10A and FIG. 10B are top-down views of templates 400 used to formexample U-shaped tabs in a sheet 410 of spacer material. The outline ofindividual tabs 320 are shown on sheet 410 and the template has ageometry that keeps the material waste to a minimum when the sheet iscut to form the tabs. The holes 354 in the tabs 320 are not shown forease of illustration, though they can be formed in sheet 410 prior tocutting to form the tabs. The cutting of sheet 410 can be accomplishedusing conventional means known in the art, such as using mechanicalcutting (e.g., computer numerical control (CNC) cutting) or laser-basedcutting. In an example, the tabs 320 can be further processed onceformed. For example, a polishing process (e.g., laser polishing) can beused to round off or otherwise smooth the edges or corners of the tabs.

FIG. 11 is a front-on close-up view of an example squared-off U-shapedtab 320. The tab 320 includes an upper edge 362, a lower edge 364,opposite sides 368, holes 354 and recess 322 formed in the lower edge.The recess 322 is defined by two tab sections 321 adjacent respectivesides 368 and also defines the downward facing ledge 352. FIG. 11 alsoshows a number of important dimensions, including: a center-to-centeralignment-feature spacing SA, an alignment feature diameter dA, anoverall width WT, an overall height HT, a recess width WR, and anintermediate height HR defined by recess 322. The tab sections 321 havea width WTS. A general dimension “x” is also denoted. In an example, HRis equal to x, the width WTS of the tab sections 321 are also equal tox, WR is equal to 2x, SA is equal to 3x, and WT is equal to 4x.

In an example where receptacle 300 is configured to mate with plug 200having a standard MT ferrule 201, the alignment feature spacing SA is4.6 mm and the alignment feature diameter dA is 0.7 mm. Nominally, thealignment features 354 are centered in the middle of respective tabsections 321, which is a spacing of 3x, so 3x is about 4.6 mm. However,the alignment features 340 can be be larger or smaller. If larger, thereneeds to be clearance from the edge of the alignment feature 354 to theadjacent edge 368, so that 4x≥4.6+1.4 mm.

Additionally, the array 230 of optical fibers 232 and the array 30 ofwaveguides 32 need to fit within recess 322. For standard MTPconnectors, the optical fiber pitch p_(F) is 250 microns and there are12 fibers, so that the recess width WR can be 2.75 mm. This means that2x>2.75 mm. Finally, alignment features 240 needs to fit inside therespective tab sections 321, so x≥0.7 mm. This is a tighter constraintthan the “2x” requirement and nominally at least 0.15 mm of materialshould be between alignment hole 240 and the adjacent side 368 so thatx≥1 mm. This also satisfies the “3x” and “4x” criteria. A nominal valueof x is 1.5 mm. For an alternate, more compact design, the fiber pitchp_(F) can be reduced to be in the range from 100 microns to 125 microns.For a fiber pitch p_(F)=125 microns, the above dimensions for tab 320,including the diameter dF of alignment hole 340, can be reduced by half,thereby making x between 0.5 and 0.75 mm.

In an example, a glass fusion process can be used to form sheet 410 as aglass sheet. As noted previously, the precision of hole 354 need nothave submicron accuracy.

Plug and Receptacle Alignment

Alignment of plug 200 and receptacle 300 can performed passively byusing alignment fiducials 374 (see FIG. 1). The alignment may also bedone actively by measuring the amount of optical power transmittedthrough waveguides 32 to optical fibers 232 in either direction (e.g.,light traveling from PIC 20 to fibers 232 or vice versa). Activealignment can also be performed by having a dedicated loop-back circuitwherein light is injected into PIC 20 and detected remote to the PIC.Passive alignment can be performed by using machine vision or opticalalignment techniques known in the art.

Once optimal alignment is achieved, then an epoxy bond (UV or thermal)or a laser bonding process can be performed using securing material 380as described above. The result is an aligned optical interface device100 that can be connected and disconnected in a manner similar if notidentical to electrical interface devices, e.g., electrical connectors.

It will be apparent to those skilled in the art that variousmodifications to the embodiments of the disclosure as described hereincan be made without departing from the spirit or scope of the disclosureas defined in the appended claims. Thus, the disclosure covers themodifications and variations provided they come within the scope of theappended claims and the equivalents thereto.

What is claimed is:
 1. A coupling device for a photonic integratedcircuit (PIC) assembly, the coupling device comprising: a bodycomprising a front end, an upper surface and a lower surface; at leastone alignment feature at the front end of the body; and a tab at thefront end of the body, the tab comprising a first downwardly dependingtab section and a second downwardly depending tab section that extendbeyond the lower surface, wherein the tab defines a recess.
 2. Thecoupling device of claim 1, wherein the tab has a U-shape.
 3. Thecoupling device of claim 1, wherein the recess is an aperture within thetab.
 4. The coupling device of claim 1, wherein the at least onealignment feature is at least one of a hole and a slot.
 5. The couplingdevice of claim 1, wherein the at least one alignment feature comprisesa hole and a slot.
 6. The coupling device of claim 1, wherein the tab isintegrally formed with the body.
 7. The coupling device of claim 1,wherein the tab is secured to the front end of the body by a securingmaterial.
 8. The coupling device of claim 7, wherein the tab comprisesat least one tab alignment feature that is aligned with the at least onealignment feature at the front end of the body.
 9. The coupling deviceof claim 1, wherein the lower surface of the body comprises one or morerecesses for receiving a securing material.
 10. The coupling device ofclaim 1, wherein the body comprises one or more through holes betweenthe upper surface and the lower surface for receiving a securingmaterial.
 11. An optical interface device comprising: the couplingdevice according to claim 1; a PIC assembly comprising: an uppersurface; a front end; and a PIC that supports at least one waveguidecomprising an end face at the front end of the PIC assembly, wherein thecoupling device is coupled to the PIC assembly such that the lowersurface of the body is coupled to the upper surface of the PIC assemblyand the tab covers at least a portion of the front end of the PICassembly.
 12. The optical interface device of claim 11, furthercomprising a substrate comprising an upper surface and a front end,wherein: the PIC assembly comprises a lower surface that is coupled tothe upper surface of the substrate; and the tab covers at least aportion of the front end of the substrate.
 13. The optical interfacedevice of claim 11, wherein: the body comprises a first part and asecond part; and the first part and the second part are coupled to thePIC assembly such that the first part and the second part are separatedfrom one another.
 14. The coupling device of claim 13, wherein the firstdownwardly depending tab second and the second downwardly depending tabsection are separate components.
 15. The coupling device of claim 13,wherein the tab is a unitary tab that extends between the first part andthe second part.
 16. An optical interface device comprising: a photonicintegrated circuit (PIC) assembly comprising: an upper surface; a frontend; and a PIC that supports at least one waveguide comprising an endface at the front end of the PIC assembly; a body comprising a front endand a lower surface; and a tab secured to the front end of the body,wherein: the tab extends beyond the lower surface; the tab definesdefine a downward facing ledge; and the tab covers at least a portion ofthe front end of the PIC assembly.
 17. The optical interface device ofclaim 16, wherein the tab comprises a first downwardly depending tabsection and a second downwardly depending tab section that define arecess.
 18. The optical interface device of claim 17, wherein the tabhas a U-shape.
 19. The optical interface device of claim 17, wherein therecess is an aperture within the tab.
 20. The optical interface deviceof claim 16, wherein: the body further comprises at least one alignmentfeature at the front end of the body; and the tab further comprises atleast one tab alignment feature that is aligned with the at least onealignment feature at the front end of the body.
 21. The opticalinterface device of claim 16, wherein the lower surface of the bodycomprises one or more recesses for receiving a securing material. 22.The optical interface device of claim 16, wherein the body comprises oneor more through holes between the upper surface and the lower surfacefor receiving a securing material.
 23. The optical interface device ofclaim 16, wherein the tab is formed of glass.